High performance, radio frequency interconnects must be built in production quantities in order to allow engineers to experiment with different designs and determine design efficiency for various circuits. These interconnects also provide the technology for connecting high performance radio frequency interconnects such as used at microwave frequencies. Many designers use "waffle-line" technology that allows high performance radio frequency interconnects. Waffle-line is predominantly formed of metal and provides a natural shielding medium to radio frequencies and especially those radio frequencies at the microwave level. Energy is propagated along "tunnels" made of the metal "waffle" structures, and the insulated wire contained in these structures serve as a microwave or other radio frequency conductor. However, waffle-line is expensive to manufacture and demands a high labor input during manufacture and in the initial production set-up.
It is known that printed dielectric layer technology and other similar dielectric materials can be less expensive than waffle-line technology. However, dielectric layers are predominantly non-conductive and do not provide adequate shielding to any microwaves. Thus, it is difficult to form a shielded conduit for the microwaves Strip line, on the other hand, is typically formed on dielectric layers and other similar dielectric materials and includes two ground planes that act to shield the microwaves. However, even with this type of structure, conductor edges are open and form an internal "space" that can excite other modes and/or couple to other conductors.
Some strip line shielding structures for dielectric layers and other strip line conductors have used conductive columns to interconnect the ground planes. Examples includes U.S. Pat. No. 4,513,266 to Ishihara and U.S. Pat. No. 5,150,088 to Virga, et al. However, these devices do not appear to be adequate for all microwave frequencies used in a conductor, where adequate edge grounding between two ground planes would be necessary.